In dense stellar environments, stars can collide. If there is a massive black hole nearby – at the centre of galaxies – these collisions can be so energetic that the two stars are completely destroyed upon collision, leaving behind an expanding gas cloud. While the collision itself can generate a very luminous flare for several days, there might be an even brighter flare that can last up to many months, as the gas cloud is captured by the nearby black hole. A research team led by MPA has estimated the observables of such powerful events for the first time using the two state-of-the-art codes AREPO and MESA, developed at MPA. more

Throwing one star into another into another star does not bode well for either star. However, given the right conditions and the right types of stars this can lead to the stars merging and forming one single object. If one of the stars is a neutron star (the dense stellar remnant after a supernovae) it can sink to the center of the other star replacing that star’s core. Such objects are called Thorne-Żytkow objects (TŻOs) as they where first proposed by Kip Thorne and Anne Żytkow. Now an international team of astrophysicists led by the Max Planck Institute for Astrophysics (MPA) has re-evaluated what these TŻOs look like and whether we can find them. more

Neutrinos are the driving factor for core-collapse supernovae, the violent death of massive stars. According to the neutrino-driven mechanism they are responsible for transferring energy from the hot proto-neutron star (PNS) to the surrounding material. So far, numerical simulations assumed that neutrinos retain their flavor during propagation. Max Planck researchers have now shown that allowing for flavor conversions has a direct influence on the supernova dynamics. more

Dark matter, which makes up over 80% of the mass in the Universe, does not absorb or emit light, interacting with light and normal (baryonic) matter only through its gravitational pull. The nature of dark matter is one of the major open questions in astrophysics and cosmology. One theoretical model for dark matter, known as fuzzy dark matter (FDM), is predicted to leave a very specific imprint on light that is bent around a massive galaxy in a phenomenon called gravitational lensing. By examining the radio light in a gravitational lens system observed at extremely high angular resolution, we have determined just how “fuzzy” the dark matter can be. more

A universal sign of higher intelligence is communication. However, not all communications are well-intentioned. How can an intelligent system recognise the truthfulness of information and defend against attempts to deceive? How can a egoistic intelligence subvert such defences? What phenomena arise in the interplay of deception and defence? To answer such questions, researchers at the Max Planck Institute for Astrophysics in Garching, the University of Sydney and the Leibniz-Institut für Wissensmedien in Tübingen have studied the social interaction of artificial intelligences and observed very human behaviour. more

Observing a supermassive black hole in the distant Universe, MPA astronomers have discovered that it is in the process of stripping gas from a neighbouring galaxy. The gas is being very quickly turned into stars in the black hole’s host galaxy and is allowing the black hole to grow very quickly. This agrees with theoretical predictions that massive galaxies and black holes form with help from mergers with smaller galaxies and bursts of star formation. more

Black holes, resulting from the death of massive stars, are some of the most exotic and powerful objects in the Universe. Since even light cannot escape these objects, the quasi-periodic signals coming from the gas falling into the black hole serve as a probe to infer a great deal of information about the black hole and its surrounding environment. The most-commonly observed quasi-periodic signal is thought to originate from the wobbling of hot gas around the black hole, like a spinning top. One problem, though, is that inferred size of this (isolated) corona seemed to be inconsistent with estimations from other observables. With our recent, state-of-the-art computer simulations, involving a more realistic geometry of the accretion flow, we demonstrated for the first time, that the presence of a disc around the corona significantly slows down its precession, relieving much of the tension between this model and observations. These results thus have important implications for studies of black hole properties and how black hole systems form and evolve. more

The universe today is host to a vast network of galaxies and an even richer array of invisible dark matter structures. But this was not always the case. The universe was nearly uniform until a time of about 100 million years, when the first cosmic structures gravitationally condensed. These objects were made of dark matter alone and each may have weighed no more than the Earth. Most of these objects do not last long: they rapidly grow and cluster together to form the much larger systems that we know today. Despite this, scientists at MPA have discovered in high-resolution simulations that some unique features of the first structures survive this process. Their lingering imprint could manifest itself in astronomical observations, yielding clues to the identity of dark matter. more

Einstein’s General Theory of Relativity predicts that large concentrations of mass – such as galaxies – will bend light rays passing nearby, a phenomenon known as gravitational lensing. When a distant galaxy (the lens) lies exactly between us and an even more distant object (the source), the source is distorted and magnified into several images around the lens galaxy. A group at MPA and other institutes used very long baseline radio interferometry (VLBI) to study a gravitational lens system in high resolution. This reveals extreme detail in the lensed images, and provides a new window into the physics of lens galaxies. more

All stars in galaxies form in the dense gas of the interstellar medium (ISM). Ionizing radiation from newly born massive stars and supernova explosions lets the gas shine at characteristic wavelengths of certain atoms and ions. The relative strength of such line fluxes is an important observational diagnostic to reveal the internal state and composition of the ISM. However, emission by diffuse ionized gas has different flux ratios making accurate predictions difficult. Scientist at MPA and their European collaborators have used supercomputers to simulate a realistic star forming interstellar medium and to quantify the contribution of the diffuse gas. This finding allows for a more accurate interpretation of observations also at early cosmic times when these extreme conditions are more common than in the local Universe.  more

Galaxy clusters are our universe's largest gravitationally bound systems, extending out to several million light-years and hosting up to 1000 galaxies. The matter permeating the clusters is known as the “intracluster medium” (ICM), a very hot and ionized gas (T~ 10-100 million K) emitting bright X-rays due to thermal bremsstrahlung. Scientists from MPA and the University of Heidelberg have discovered that the ICM also contains a significant amount of cool gas (10,000 K) up to large distances. The statistical connection between the haloes of cluster galaxies and absorption features points toward a complex origin of this cool gas where clouds are either associated with satellite galaxies or were previously stripped from their haloes. more

Galaxies are embedded in large reservoirs of gas - mostly hydrogen and helium. This hydrogen gas has been found to glow faintly in a specific ultraviolet wavelength, or color, called Lyman-alpha. Scientists at the MPA have discovered that these Lyman-alpha halos are larger than previously thought, spanning several 100,000 light years. The inferred size and shape of the halos suggest that the light in the outer parts of the halos comes from surrounding galaxies or the gas in their environments rather than from the central galaxy itself. more